This invention relates to an improvement in a variable magnification type optical copier in which the copying size can be increased or decreased as desired.
A conventional variable magnification type optical copier, such as shown in FIG. 1, is disclosed in U.S. patent application Ser. No. 244,476 filed Mar. 16, 1981. Briefly, the optical copier operates as follows. An original placed on a contact glass 2 on the top of the copier is illuminated by a light source 3 which reciprocates between a standby position A and a finish position B to scan the original. Upon illumination of the original, light reflected from the original is received by a full-speed mirror 6 which moves with the light source 3, and is introduced through half-speed mirrors 7 and 8 (in general, the half-speed mirrors 7 and 8 move in such a manner that the amount of displacement thereof is half of the amount of displacement of the full-speed mirror 6 in order to maintain constant an object-to-image distance for zoom lens system 9 described later) to the zoom lens system 9 incorporated in a variable magnification device 11. The reflected light thus introduced exits after being subjected to magnification variation by the zoom lens system 9 which has been moved for a specified magnification factor. Then, the reflected light is reflected by a stationary mirror 10 so as to be applied to a photo-sensitive drum 13. As a result, a magnified electrostatic latent image of the original is formed on the photosensitive drum 13. Therefore, the image is recorded in a conventional electrostatic recording process.
In such a copier, the movement region of the zoom lens system 9 overlaps the movement region of the half-speed mirrors 7 and 8. Therefore, in enlarging the image of the original, the zoom lens system 9 must be set close to the half-speed mirrors, i.e., it is moved to the left in FIG. 1 for purposes of enlargement, and accordingly the movement region of the half-speed mirrors is necessarily decreased. In the case where a copying image to be enlarged is close to the maximum original size of the optical copier, i.e. both the image size and the original size are large, several disadvantages result. For instance, if an original of size "A4" is enlarged into an image of size "A3" by a copier whose maximum permissible original size is "A3", with the longer side of the maximum copying original size as a reference as shown in FIGS. 2(a) and 2(b), and if the original 22 of size "A4" is set vertically as shown in FIG. 2(a), then the half-speed mirrors 7 and 8 can move without contacting the zoom lens system while maintaining the object-to-image distance constant, because the scanning distance of the full-speed mirror 6 is only half of the longitudinal length of size "A3". However, as the image is enlarged uniformly in all directions, including in the widthwise direction of the drum 13, a part of the image exceeds the size of the drum 13 as indicated by the phantom line; that is, this part of the image is not formed on the drum. On the other hand, if the original is set horizontally as shown in FIG. 2(b), then the amount of necessary movement of the half-speed mirrors 7 and 8 is increased to the point where they are interfered with by the zoom lens 9. Therefore, it is impossible to obtain the movement region of the half-speed mirrors which is sufficient for enlarging size "A4" into size "A3", and the image of the original is copied only on a part of the size "A3", as shown in FIG. 2(b).
In order to overcome this drawback, the width of the drum must be increased. Alternatively, the enlarging must be limited to size "A5" or "A4" although the copier can copy the image of an original of size "A3".